Filtration face masks or respirators are used in a wide variety of applications when it is desired to protect a human's respiratory system from particles suspended in the air or from unpleasant or noxious gases.
Filter elements of respirators may be integral to the body of the respirator or they may be replaceable, but in either case, the filter element must provide the wearer with protection from airborne particles or unpleasant or noxious gases over the service life of the respirator or filter element. The respirator must provide a proper fit to the human face without obscuring the wearer's vision and it is desirable that a respirator require a minimum of effort to draw air in through the filter media. This is referred to as the pressure drop across a mask, or breathing resistance.
To achieve the levels of filter performance such as those defined in 30 C.F.R. 11 subpart K .sctn..sctn.11.130-11.140-12 (1987), DIN 3181 Part 2, "Atemfilter fur Atemschultzgerate" (March, 1980), BS 2091, "Respirators for Protection Against Harmful Dusts and Gases" (1969), and BS 4555, "High Effeciency Dust Respirators" (1970) the number of layers of filter material, filter material type, and available filtration area are important factors in filter element design. The present invention provides a means of more fully utilizing a filter element's available filtration area by properly managing air flow through the filter material of the filter element. Proper management of air flow can also prevent premature loading of the filter material immediately opposite the breather or inhalation tube, which can cause the filter element to collapse over the breather tube, thereby restricting inhalation and shortening the service life of the filter element.
Various filter element designs have been proposed to provide as much filter surface area as possible while minimizing the obstruction to the wearer's vision, and/or the pressure drop across the mask. U.S. Pat. No. 2,320,770 (Cover) discloses a respirator with detachable filter elements. The filter elements are preferably rectangular and are made from a sheet of filter material with all open sides sewn closed. The filter element has a hole adapted to be attached to the body of the mask. Cover asserts that after being sewn, the filter element can be turned inside out so the seams and folds cause the bag to assume a shape and curvature which tends to keep the sides of the bags apart without the aid of an additional spacing element. Incoming air is apparently intended to travel through either the front or back sides of the bag into the space between these sides and then through the hole inside the mask. U.S. Pat. No. 2,220,374 (Lewis) discloses a respirator which includes a rigid mask and a face mold attached to the mask. The rigid mask includes an air inlet opening and filtering means covering the opening. The filtering means comprises a shell having perforations on at least three sides, filtering material located inside the shell, and a filter spreading member adapted to hold the filtering material in a position exposing the filtering material to direct contact with the air entering the perforations. U.S. Pat. No. 2,295,119 (Malcom et al.) discloses a respirator comprising a face piece adapted for the wearer's nose and mouth attached to two removable, egg-shaped filter boxes. The filter boxes have inner and outer, perforated members or covers which form a filter chamber, and two filter elements positioned between the inner and outer members of the filter box whose peripheral portions are compressed and sealed between the outer and inner members of the filter box. One of the filter elements is attached to the filter box and face piece by a locking member which secures the filter element around the air entrance opening of the face piece. Preferably, the filter box also includes a means to engage the outer filter element and space it from the inner filter element inside the filter box such as a member in the shape of a reverse curve which is part of the locking member which clamps the filter material around the air entrance opening of the face piece. U.S. Pat. No. 2,206,061 (Splaine) discloses a respirator comprising a face piece adapted to fit over the nose and mouth of the wearer which is adapted to fit into the open ends of two filters. The filters extend laterally in opposite directions from the face piece. The filters are relatively narrow, tapering from a rounded end at the bottom towards the top so that the side walls substantially meet at the top edge and contain light coil springs extending along the bottom portion of each filter to help keep the filters in an expanded condition. U.S. Pat. No. 4,501,272 (Shigematsu et al.) discloses an embodiment of a dust-proof respirator with an intake chamber assembly comprising an intake cylinder fitted airtight into a mounting mouth of a mask body with a front wall positioned opposedly to the intake cylinder and a rear wall composed of a filtration medium fastened to the intake cylinder and along the peripheral edge of the front wall. Filtration medium is also fastened to the front of the intake chamber, resulting in increased filtration area.
The present invention provides, in an easily manufactured form, a filter element of compact size and a nature capable of low air flow resistance and high filtration efficiency which satisfies various performance specifications of U.S. and foreign countries some of which have been set forth above. None of the prior art teaches a combination of features like those of the present invention having the advantages of the present invention.